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Case Study: Measures

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Point and Interval Estimates of Measures of Disease Occurrence and of Association

Measure                         Point estimate                          95% Confidence interval

Incidence rate (R)                                                                   

Prevalence (P)                                                                        

where d = number of cases, py = person-years, and T = total population

Standardized Mortality Ratio (SMR):



where SMRL and SMRU = lower and upper limits of SMR.


Types of Epidemiological Studies and their Measures of Association and Disease Occurrence

Cohort Studies


Not exposed





Point estimate

95% Confidence interval

Rate Ratio (RR)

Attributable risk in the exposed


Attributable risk per cent in the exposed


where and = lower and upper limits of RR

Population Attributable Risk (PAR)%

= rate in the total cohort

= rate in the unexposed

Unmatched case-control studies


Not exposed



Total (T)



Unmatched case-control studies (continued)


Point estimate

95% Confidence interval

Odds Ratio (OR)

Attributable Risk per cent in the Exposed


where and = lower and upper limits of OR

Population Attributable Risk (PAR)%

where = proportion of exposed controls, EF = Error Factor =

Matched case-control studies

Controls Exposed

Controls not Exposed,

Cases Exposed



Cases not Exposed



where f = frequency of pairs


Point estimate

95% Confidence interval

Odds Ratio (OR)

Attributable Risk per cent in the Exposed


where ORL and ORU = lower and upper limits of OR

Population Attributable Risk (PAR)%

Where = proportion of exposed cases, EF = Error Factor =

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Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Biological Monitoring
Epidemiology and Statistics
Occupational Hygiene
Personal Protection
Record Systems and Surveillance
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides

Epidemiology and Statistics Additional Resources

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